This thesis explores the validity in principle of educational theory. Part One examines current controversy over its status. Via the Hirst/O'Connor debate, central issues are identified: the relation of theory to practice; the logical status of prescriptive theory; the epistemic foundations of normative statements; the validity of behavioural science; the putative discreteness of empirical and normative questions in education. The presumed potential validity of the former and the supposed arbitrariness of the latter are claimed to reflect acceptance of a positivist paradigm both mistaken and unfruitful in this context. Part Two disputes philosophers' disclaimers for their substantive role in prescription, which arise in reaction against illegitimate deductions from metaphysical positions, and in conformity with the tenets of analytic philosophy. Supporting claims - that conceptual analysis reveals truths both non-empirical and value-free, and that the normative regress leaves judgements unsupported - are questioned. Analysis simply clarifies conditions for conceptual revision whilst the normative regress similarly implies a coherence theory of truth only mistakenly equated with irrationality. Part Three disputes the corollary that empirical questions in education are discrete and logically unproblematic. After establishing the logical and methodological characteristics of behavioural enquiry, the assumptions, procedures and findings of a large-scale positivist research project are examined to show that this approach to empirical work in education is as necessarily distorting and supportive of theorists' ideology as is exclusive reliance on conceptual analysis in normative theorising. Increased validity in educational theory is argued to depend on rejection of positivist norms of rationality and on adoption of a more tentative, piecemeal approach which admits an anthropomorphic model of man, the relevance of practical knowledge and the functional interdependence of factual and normative enquiry.